Property crimes, such as theft, burglary, and arson, make up an overwhelming majority of all crimes. Property criminals are often recidivists. According to data from the Virginia State database, 32% of the violent crimes solved in Virginia were committed by individuals with previous property crime convictions. (See, Ban, J. Cambridge Healthtech Institute's Fifth Annual DNA Forensics. Washington D.C., Jun. 27-28, 2002.)
Fingerprints were first used in the United States by the New York prison system in 1903. Although, it is often considered by many as a “low-tech” crime-solving method because it entails subjective visual examination, it is a highly reliable and accessible means of obtaining evidence at a crime scene. Today, the fingerprinting technique incorporates highly sophisticated state of the art technologies. To date, the FBI has a large collection of fingerprints, totaling millions, which have been used by law enforcement agencies to identify defendants and crime victims by matching prints from crime scenes with those on file.
The basic principle behind the use of fingerprint evidence are based on, (1) a person's “friction ridge patterns” or swirled skin on his/her fingertips do not change, and (2) no two persons have the same pattern of friction ridges. Since the friction ridges contain rows of sweat pores, fingerprints are often produced when the sweat from these ridges mixed with other body oils and dirt. The visibility of the prints is enhanced only when powders and chemicals are dusted onto the surface and excess powder brushed away, lifted from the surface using tapes or photographed and then compared to fingerprints in a database. Prints may be visible with alternate light sources or with the naked eye depending upon the surface and the situation. For example, in a humid environment, more moisture on the skin would allow for a more visible print.
The quality of the prints, therefore, depends on the type of surfaces from which they are lifted. Furthermore, fingerprints are often lost with time or through contamination by the first responders (e.g., a fingerprint collector) at the scene of crime, resulting in the destruction or rendering useless of valuable evidences. In addition, because it is almost impossible to determine the age of a set of fingerprints, defendants often attempt to testify that they were present prior to the crime and the prints were left at a time other than at the time of the crime. Although computer enhancement laser techniques have been employed to extrapolate complete prints from mere fragments and invisible markings respectively, there is still a need for a better and more sensitive method of identifying the perpetrator.
The use of DNA analysis or typing has proven to be a revolutionary and powerful method for solving crimes, particularly in violent crimes since the introduction of fingerprinting a century ago. Being the genetic blueprint, each individual's DNA is unique to them except for identical twins. As such, DNA analysis is a highly discriminating method of identifying individuals. The value of forensic DNA analysis is enormous, particularly, with the creation of a national DNA database management system, known as CODIS (Combine DNA Index System) set up by the FBI and the U.S. Department of Justice. CODIS contains DNA profiles from biological evidence collected from crimes scenes as well as from convicted offenders. The profile generated from an evidentiary sample may be searched against the profiles contained in CODIS, in order to link evidence from other crimes to the case, or if no suspect is known, to a matching profile from a previous offender. Therefore, evidence from different crime scenes can be compared to link the same perpetrator to multiple crimes locally, nationally or internationally. Furthermore, the DNA molecule is very stable and can withstand significant environmental insults or challenges, thus allowing information to be collected from old biological samples or badly degraded samples.
Forensic DNA samples are usually collected from blood, saliva, semen, and other bodily fluids by wiping onto a cotton-tipped swab or a cotton pad. Other sources include hair, bones, skin etc. The evidence-containing swabs or pads are placed into plastic or paper container or bag for future analysis. One of the major disadvantages of using a cotton-tipped swab or cotton pad is that elution of small samples from the cotton-tipped swab or cotton swab can be inefficient in recovery and release of DNA, particularly when the amount available is small to begin with. Furthermore, the amount of sample evidence may be contaminated or diminished when the swab or pad comes in contact with the container or bag.
DNA samples are extracted, PCR-amplified and traditionally analyzed by restriction fragment length polymorphism (RFLP). RFLP is a technique by which an individual of a species can be differentiated by the banding pattern of DNA fragments obtained by subjecting DNA to restriction enzyme cleavage. (See, Wyman, A. R and White, R., Proc. Natl. Acad. Sci. USA 77, 6754 (1980)). The unique banding patterns of the DNA fragments are then separated by gel electrophoresis and detected by Southern blot analyses using a radioactive probe for a particular locus of the human chromosome, such as the D14S1 locus, which serves as a polymorphic marker unique to an individual. Two major disadvantages of the RFLP technique are the requirement for a substantial amount of DNA is required that is not degraded or fragmented. If a small quantity amount of DNA is analyzed, multiple cycles of amplification must be performed in order to obtain sufficient DNA for RFLP analysis. Thus, if low quantity DNA is obtained, the RFLP method can be burdensome and time consuming, in addition to the added cost in carrying out multiple PCR reactions.
More recently, the use of tandemly repeated DNA sequences, which are widespread throughout the human genome with sufficient variability amongst individuals in a population, provide still a further advancement in forensic DNA evidence analysis. Depending on the size of the tandem repeats, these tandemly repeated DNA regions may be classified as minisatellites, or variable number of tandem repeats (VNTRs) having core repeats of about 9-80 base pairs (bp) in length (See, Jeffreys, A. J., et al., Nature 316, 76 (1985)) or microsatellites, or short tandem repeats (STRs) with about 2-5 bp repeats (See, Weber, J. L. and May, P. E., Am. J. Hum. Genet. 44, 388 (1989); Edwards, A., et al., Am. J. Hum. Genet. 49,746 (1991) and Polymeropoulos, M. H. et al., Nucl. Acids. Res. 19, 4018; and id. 4306m (1991)).
Although STRs have the same basic structure as VNTRs, the tandemly repeated sequences of 2-5 bp make the STR markers more compatible with the use of PCR. In addition, only a limited number of selected STR markers that are useful for human identification are required in forensic analyses compared to the thousands that are available. Criteria for selection of STR markers include (1) high degree of variability within the population, (2) easily distinguishable amplified products, (3) low prevalence of stutter bands, which are amplification artifacts that are one or more repeat lengths above or below the true amplified alleles, and (4) low mutation rates. (See, Weber, J. L. and May, P. E., Am. J. Hum. Genet. 44, 388 (1989); Levinson, G. and Gutman, G. A., Mol. Biol. Evol. 4, 203 (1987) and Schlotterer, C. and Tautz, D., Nucl. Acids. Res. 20, 211 (1992)). Thus, STR systems that are currently being developed must have high discrimination potential with minimal genetic artifacts, such as microvariants, and minimal amplification artifacts, e.g. stutter bands. Many STR loci are in development as genetic markers for forensic purposes with several more to be expected. (See, Schumm, J. W., Notes Magazine 58, 12 (1996) Promega).
Both the fingerprinting and DNA typing methods are powerful means currently used for solving crimes. Thus, combining both these methods may prove to be a major advance in the field of forensic science for the detection and identification of suspects, with a low possibility of mistaken identities. However, both methods require a means of collecting forensic evidence at the crime scene that are not compromised and the method must also be efficient in yielding small amounts of DNA, typically about 1 ng or less. For analysis of DNA, the yield must be sufficient to allow identification of a sufficient number of genetic features from a fingerprint to allow confident matching with an alleged perpetrator. Typically, matching is done by determining a minimum number of identifiable STR loci from a standard set of loci. At each locus, two alleles are expected, one from each chromosome of an individual. The identification is made difficult by allele drop-outs (e.g., in a heterozygote, only one allele is apparent at a locus) and drop-ins (more than two alleles are apparent). The current method of collecting DNA samples using cotton-tipped swab or cotton pad does not provide for an efficient method of collecting samples from a fingerprint, which may contain fewer than two cells or picograms (pg) quantities of DNA. An efficient and reliable method for recovery of forensic DNA from fingerprints, and release by extraction that allows analysis of the low copy number DNA is therefore highly desirable.